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DUPLTC       - 

BULLETIN  No.  124  OCTOBER  1916 

GEORGIA  EXPERIMENT  STATION 

EXPERIMENT,  GEORGIA 


The  Two  Groups  of  Varieties  of  the  Hicora  Pecan 

and 

Their  Relation  to  Self-Sterility 

By  H.  P.  STUCKEY 


The  Bulletins  of  this  Station  are  sent  free  to  all  "persons  actu- 
ally engaged  in  farming  who  make  request  for  same,"  and  all 
newspapers  in  the  State.  Address 

R.  J.  H.  DeLOACH,  Director,  Experiment,  Ga. 


RURAL1ST  PRESS,  Inc.-3524 


ORGANIZATION 


Board  of  Directors 


HOX.  j.  D.  PRICE 

Commissioner  of  Agriculture,  Ex-Officio  President  of  Board,  Atlanta,  Ga. 

D.  C.  BARROW,  C.  &  M.  E.,  LL.  D. 
Chancellor  of  the  University  of  Georgia,  Ex-Officio  Member,  Athens,  Ga. 

ANDREW  M.  SOULE,  B.  S.  A.,  Sc.  D. 

President  State  College  of  Agriculture  and  Mechanic  Arts,  Athens,  Ga. 
Designated  by  the  Governor. 

FIRST  DISTRICT 

R.  C.  NEELY    Waynesboro 

SECOND  DISTRICT 

J.  W.  ANDREWS    Carnegie 

THIRD  DISTRICT 

W.   D.   HAMMACK Coleman 

FOURTH  DISTRICT 

J.   H.   MOBLEY    Hamilton 

FIFTH  DISTRICT 

JOHN  T.  DUNCAN   Douglasville 

SIXTH  DISTRICT 

J.  J.  FLYNT   Griffin 

SEVENTH  DISTRICT 

JOHN  W.  L.  BROWN  Cartersville 

EIGHTH  DISTRICT 

B.  W.  HUNT  Eatonton 

NINTH  DISTRICT 

L.  G.  HARDMAN,  M.  D Commerce 

TENTH  DISTRICT 

A.  S.  CHAMLEE   : Bartow 

ELEVENTH  DISTRICT 

WILLIAM  HENDERSON    Ocilla 

TWELFTH  DISTRICT 
F.  R.  MANN Jacksonville 


Station  Officers 

R.  J.  H.  DELOACH    Director 

H.  P.  STUCKEY  Horticulturist 

J.  C.  TEMPLE  Bacteriologist 

P.  V.  EWING  Animal  Husbandman 

C.  A.  WELLS   Chemist 

B.  B.  BIGGINS  Botanist  and  Plant  Pathologist 

c.  K.  MCCLELLAND  Agronomist 

F.  H.  SMITH  Assistant  Chemist 


The  Two  Groups  of  Varieties  of  the  Hicora 
Pecan  and  their  Relation  to  Self-Sterility 


H.  P.  STUCKEY 


Some  form  of  sterility  in  plants  as  the  cause  of  much  poor  bearing  has 
occupied  the  attention  of  horticulturists  since  the  publication  of  Darwin's 
work  in  1862  on  the  various  contrivances  by  which  orchids  are  fertilized  by 
insects.  Since  then,  few  horticultural  plants  of  any  consequence  have 
escaped  notice  in  these  searching  investigations  and  many  results  of 
economic  importance  have  been  accomplished.  Beach  (3),  Bailey,  (2), 
Waite  (4)  and  Waugh  (5)  were  among  the  first  horticultural  investi- 
gators in  this  country  to  do  systematic  work  on  sterility  in  horticultural 
plants.  This  has  been  constantly  added  to  by  many  other  workers  in  later 
years. 

As  nut  trees  became  of  commercial  importance,  whether  or  not  they  are 
self-sterile  became  an  important  problem.  However,  little  work  so  far  has 
been  done  along  this  line.  Lewis  (10)  states  that  Persian  walnut  trees 
from  four  to  six  years  old  often  start  a  heavy  crop  of  nuts  only  to  have 
them  drop  before  maturity.  "This,"  he  says,  "is  due  to  the  fact  that  young 
walnut  trees  do  not  produce  sufficient  catkins  and  therefore  do  not  have  a 
sufficient  quantity  of  pollen.  After  the  trees  become  older  there  seems  to 
be  less  trouble  from  this  source.  With  the  young  Froquette  trees,  it  is 
especially  noticeable  that  the  catkins  are  scarce  the  first  few  years,  but  by 
the  time  the  trees  reach  the  period  of  heavy  bearing,  at  seven  years,  there 
are  generally  sufficient  catkins  to  insure  a  good  crop.  With  the  Magette, 
the  female  blossoms  sometimes  appear  before  the  male,  while  with  the 
Gladys,  they  are  both  apt  to  appear  together." 

Itamsey  (8)  working  with  other  varieties  of  Persian  walnuts  finds  simi- 
lar conditions. 

No  work  has  been  done  on  self-sterility  in  pecans,  the  only  record  found 
is  that  by  Berckmans  (9)  who  states  that  sometimes  staminate  flowers  of 
pecans  appear  before  the  pistillate  flowers,  causing  poor  crops  of  nuts. 
However,  he  gives  no  data  on  the  subject. 

In  the  past  eight  years  during  which  we  have  been  working  with  the 
pecan,  reports  and  inquiries  have  come  to  us  from  various  sections  of  this 
state  and  from  other  states  in  regard  to  single  trees  or  isolated  groups  of 
trees  of  a  single  variety  that  were  shy  bearers  or  that  did  not  bear  at  all. 
This  raised  the  question  of  whether  or  not  some  varieties  of  pecans  were 
not  partially  or  wholly-  self-sterile. 


233133 


128 


GEORGIA  EXPERIMENT  STATION 


Twig  on  left  from  Group  I.     Twig  on  right  from  Group  II.     Note 
how  the  Catkins  of  Group  I  protrude  while  the  buds  are  still  small. 


Two  GROUPS  OF  THE  HICORA  PECAN  129 


The  Two  Groups  of  Hicora  Pecan  and  Their 
Distinguishing  Characters 

In  our  work  with  the  Hicora' Pecan,  we  found  that  the  varieties  easily 
fall  into  two  distinct  groups  (1)  which  bear  a  close  relation  to  the  problem 
of  self-sterility.  These  two  groups  are  easily  distinguished  from  each  other 
by  the  floral  characters  of  the  catkins  of  staminate  flowers ;  and  also,  by 
the  difference  in  development  of  the  pollen  grains  of  the  two  groups. 

In  Group  I,  the  embryonic  catkins  of  staminate  flowers  are  enclosed  in 
rather  short,  broad,  bud  scales,  one  on  each  side  of  the  leaf  bud.  The 
catkins  themselves  are  rather  short  and  broad  as  compared  with  their 
length,  and  the  individual  flowers  of  the  catkins  are  shielded  by  short, 
rather  small  and  inconspicuous  bracts.  The  catkins  of  Group  I  protrude 
from  one  to  five  days  before  those  of  Group  II  protrude,  and  shed  their 
pollen  from  five  to  ten  days  before  those  of  Group  II.  With  most  of  the 
varieties  of  this  group,  the  pistillate  flowers  become  receptive  at  about  the 
same  time  that  the  staminate  flowers  shed  their  pollen.  However,  a  few 
varieties  of  this  group  have  a  considerable  percentage  of  their  pistillate 
flowers  to  become  receptive  after  the  maximum  dehiscence  of  pollen. 

In  Group  II,  the  embryonic  catkins  of  staminate  flowers  are  enclosed 
in  long  and  rather  slender  bud  scales.  These  catkins  are  usually  narrower 
and  longer  than  those  of  Group  I  and  the  individual  flowers  are  shielded  by 
long,  narrow,  conspicuous  bracts.  '  (Fig.  2.)  In  this  group,  the  pistil- 
late flowers  beqome  receptive  from  two  to  ten  days  before  the  staminate 
flowers  shed  their  pollen ;  and,  in  most  cases,  a  large  percentage  of  the 
stigmas  of  the  pistillate  flowers  have  become  dried  or  calloused  before  the 
pollen  is  she*!. 

The  differences  and  some  of  the  characteristics  of  the  two  groups  is 
shown  in  the  following  tables,  which  gives  some  of  the  varieties  grown  on 
the  Station  grounds  in  1915  and  1916: 


130 


GEORGIA  EXPERIMENT  STATION 


Two  GROUPS  OF  THE  HICORA  PECAN 


131 


TABLE  No.  I 

GROUP  I 

Variety 
Alley 

Date 
stigmas, 
receptive 

5/1 

5/1 

Centennial  
Mobile  
Mantura  
Nelson  
Pabst  . 

4/30 
5/1 
5/1 
4/30 
4/30 

Randal 

5/1 

Rome 

4/30 

Jerome 

4/30 

Robson  
San  Saba  

4/30 
4/30 

Date 

first  pollen 
shed 
5/1 
5/1 
5/1 
5/1 
4/30 
4/28 
5/1 
5/1 
4/30 
5/1 
5/1 
5/2 


•Percent  pollen 
germination 


GROUP  II 


Variety 
Appomattox    . . 

Atlanta    

Bradley    

Curtis    

Frotscher  .... 
Moneymaker  . 
Pan  American 

President    

Russell    

Stuart   

Teche    

Van  Deman  . . 
Younjr  


Date 
stigmas 
receptive 
4/30 
5/1 
4/30 
4/30 
4/30 
4/30 
4/30 
4/30 
4/30 
4/30 
4/30 
4/30 
4/30 


Date 

first  pollen 
shed 
5/5 
5/10 
4/9 
5/13 
5/10 
5/6 
5/9 
5/9 
5/6 
5/6 
5/8 
5/9 
5/9 


Date 

Percent 

stigmas 
dried 

pollen 
germination 

5/5 

15 

5/5 

40 

5/5 

35 

5/7 

40 

5/6 

40 

5/3 

20 

5/5 

40 

5/5 

15 

5/5 

5/5 

20 

5/5 

50 

5/5 

.5 

5/5 

15 

Phonological  Data  for  1916 


In  1916  an  effort  was  made  to  get  more  complete  phenological  data  from 
the  Station  orchard  as  well  as  from  a  number  of  varieties  of  pecans  grown 
in  commercial  orchards  in  the  southern  part  of  the  state. 

To  eliminate,  so  far  as  practicable,  individual  variations,  more  than  one 
tree,  of  most  varieties,  were  used  in  the  1916  records.  In  the  following  tables 
both  groups  of  varieties  are  given,  but  the  group  number  of  each  is  indicated 
by  numbers  1  or  2.  instead  of  the  groups  being  made  into  separate  tables. 


132 


GEORGIA  EXPERIMENT  STATION 


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Two  GROVPS  OF  THE  HICOBA  PECAN 


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GEORGIA  EXPERIMKNT  STATION 


stiiiuiiiute  and  pistillate  flowers  from  a  Pan-American  tree.     The  stigmas  hav« 
dried  and  nut  growth  started,  while  no  pollen  has  been  shed  from  the  Catkins. 


Two  GROUPS  OF  THE  HICOEA  PECAN 


135 


In  Group  I  of  the  1915  table,  it  will  be  observed  that  the  pollen  shed  at 
about  the  same  time  the  pistillate  flowers  became  receptive.  This  is  very 
important  in  its  bearing  upon  the  question  of  whether  or  not  those  varieties 
are  self-sterile. 

In  Group  II  of  the  1915  table,  it  will  be  noticed  that  the  interval  between 
the  receptive  stage  of  the  stigmas  and  the  first  shedding  of  the  pollen  is 
much  greater  in  this  group  than  in  Group  I.  In  fact  it  was  observed  that 
one  Moneymaker  and  one  Van  Deman  tree  had  dried  stigmas  and  young 
nuts  had  started  into  growth  before  the  first  pollen  had  shed  off  these  two 
trees,  respectively.  Further,  most  of  the  stigmas  of  the  different  varieties 
of  Group  II  had  dried,  showing  that  they  were  past  the  receptive  stage, 
before  the  first  pollen  was  shed. 

The  percentage  of  pollen  germination  in  Group  I  was  very  low  in  1915. 
In  making  the  germination  tests  of  the  pollen,  only  one  trial  was  given  each 
variety  merely  to  determine  whether  the  pollen  was  capable  of  germination. 
Further  trials  made  under  even  slightly  changed  conditions,  would  probably 
have  given  different  percentages  of  germination,  for,  as  will  be  seen  later, 
Group  I  gave  in  1916  a  much  higher  percentage  of  pollen  germination, 
which  was  about  equal  to  that  of  Group  II  of  that  year. 

In  the  1916  table,  it  will  be  noticed  that  those  varieties  marked  Group  I 
shed  their  pollen  at  about  the  same  time  the  pistillate  flowers  became  re- 
ceptive as  was  observed  in  the  1915  table,  while  those  varieties  marked 
Group  II,  showed  a  like  interval  to  Group  II  of  the  1915  table,  between  the 
receptive  stage  of  the  pistillate  flowers  and  the  shedding  of  the  pollen. 

The  percentage  of  pollen  germination  in  Group  I  of  1916  was  about 
equal  to  that  of  Group  II. 

Phonological  Data  from  South  Georgia  for  1916 

To  determine  the  behavior  of  a  number  of  varieties  under  different  cli- 
matic and  soil  conditions  we  secured  the  co-operation  of  a  few  pecan  grow- 
ers in  the  southern  part  of  the  state  where  the  conditions  are  thought  to 
be  more  favorable  to  pecan  growing  and  where  large  commercial  orchards 
have  been  planted. 

Below  are  given  some  data  for  1916  on  a  large  number  of  varieties,  at 
Cairo,  Ga.,  supplied  us  by  Mr.  J.  Stater  Wight,  of  that  place : 

TABLE  No.  HI 


Variety 

Nelson    

Mantura    

Waukenah   

Alley    

Van  Deman    

Schley    

Frotscher  

Teche    

Moore    

Curtis    

Delmas   

Mobile  

Lott  No.  3 

Success  

Pabst 

Lott   No.    2 

Moneymaker   

Stuart   

Oliver    

Centennial    

Georgia  Giant 


Variety 
group 

1 

1 

2 

1 
2 

2 
2 
2 
1 
2 
2 
1 
2 
1 
1 
2 

2 
2 
1 
1 
1 


Date  pistils 
receptive 
4/14 
4/15 
4/20 
4/22 
4/24 
4/26 
4/24 
4/24 
4/21 
4/26 
4/26 
4/25 
4/28 
4/28 
4/29 
5/2 
4/24 
5/2 
4/29 
5/1 
4/28 


Date  first 
pollen  shed 

4/14 

4/16 

4/29 

4/22 

5/3 

4/29 
-   5/2 

5/1 

4/22 

5/6 

5/3 

4/26 

5/5 

4/30 

4/20 

5/7 

5/1 

5/9 

4/30 

5/1 

4/28 


Days 
difference 
0 

1 


130 


GEORGIA  EXPERIMENT  STATION 


To  determine  the  variation  in  time  of  blooming  within  the  variety,  Mr. 
Wight  furnished  the  following  data  on  Frotscher,  Moneymaker,  Wankenah, 
Teche  and  Stuart  varieties: 

FROTSCHER  WAUKENAH 

5  trees  shed  first  pollen  April  2nd.  5  trees  shed  first  pollen  May  3rd. 

76  trees  shed  first  pollen  April  3rd.  3  trees  shed  first  pollen  May  4th. 

26  trees  shed  first  pollen  April  4th.  TECHE 

13  trees  shed  first  pollen  April  5th.  3  trees  shed  first  pollen  May  5th. 

10  trees  shed  first  pollen  April  6th.  2  trees  shed  first  pollen  May  6th. 

5  trees  hsed  first  pollen  April  7th.  a  tree  shed  flrst  pollen  May  7th. 

MONEYMAKER  STUART 

8  trees  shed  first  pollen  May  1st.        a  tree     shed  first  pollen  May  8th. 
1  tree     shed  first  pollen  May  5th.        6  trees  sned  first  pollen  May  9th. 

1  tree  shed  first  pollen  May  10th. 

It  will  be  observed  that  the  difference  in  dates  of  blooming  and  the  inter- 
val between  the  receptive  stage  of  the  pistillate  flowers  and  the  shedding 
of  the  pollen  of  the  two  groups  of  varieties  grown  at  Cairo,  in  South  Geor- 
gia, are  very  similar  to  these  differences  between  the  two  groups  of  varieties 
grown  at  Experiment — in  north  middle  Georgia.  The  essential  difference 
is  that  the  varieties  of  both  groups  shed  pollen,  on  the  average,  about 
ten  days  earlier  at  Cairo  than  at  Experiment.  This  difference  is  very  vari- 
able, ranging  from  one  to  fifteen  days,  which  may  be  due  to  a  difference 
in  strain  of  varieties  or  the  possibility  of  some  varieties  being  misnamed  at 
one  or  the  other  locations. 


Pecan   pollen   grains  greatly   enlarged — from  the   Alley  variety. 

Differences  in  Development  of  Pollen  of  the  Two  Groups 

In  size,  shape,  and  general  characters,  the  pollen  of  the  two  groups  of 
varieties  of  pecans  differ  almost  none.  But  there  is  a  difference,  however, 
in  the  time  or  rapidity  of  the  development  of  the  pollen  of  the  two  groups. 


Two  GROUPS  OF  THE  HICORA  PECAN 


137 


In  general,  pecan  pollen  is  somewhat  spherical  and  rather  flattened  in 
shape.  It  is  rather  large  in  comparison  with  pollen  from  other  nuts, 
being  of  practically  the  same  size  as  that  of  hickory,  considerably  larger 
than  pollen  of  Japan  walnuts,  and  larger  still  than  that  of  the  Spanish 
Chestnut. 

Pecan  pollen  grains  have  from  three  to  five  germ  pores;  and  usually,  in 
germinating,  send  out  a  tube  through  one  pore.  However,  sometimes  the 
pollen  grains  send  out  more  than  one  tube.  *The  pollen  mother  cells,  tetrads, 
and  pollen  grains  form  first,  respectively,  at  the  basal  end  of  the  catkins  of 
stamina te  flowers.  Here,  also,  the  pollen  begins  to  shed  first.  The  pollen 
formed  at  the  distal  end  or  apex  of  the  catkins  is  often  almost  void  of  germ 
pores  and  not  infrequently  shows  signs  of  degeneration  in  the  nuclei. 

In  the  development  of  the  pollen  in  Group  I,  the  average  difference  in 
time  between  the  tetrad  stage  and  pollen  formation  was  approximately  two 
days,  while  for  Group  II  the  average  was  approximately  two  and  one-half 
days. 

In  Group  I  the  average  time  between  the  pollen  formation  and  the  first 
shedding  of  pollen  was  approximately  fifteen  days,  while  that  of  Group  II 
was  eighteen  days ;  further  these  intervals  vary  less  than  do  the  intervals 
between  the  appearance  of  the  catkins  and  the  tetrad  stages  of  the  two 
groups. 


SMC 


Germinating  pollen  from  the  Nelson  variety. 

*  NOTE — Normal  pollen  formation  in  pecans  is  the  same  as  that  in  most  other 
seed-producing  plants. 

Within  the  embryonic  anthers  are  formed  pollen  mother  cells.  Within  each  of 
those  pollen  mother  cells  four  pollen  grains  are  formed.  The  mother  cell  containing 
the  four  miscrospores  or  pollen  grains  is  called  a  tetrad. 


13* 


GEORGIA  EXPERIMENT  STATION 


A  tetrad   greatly   enlarged — from 
the  Jerome  variety. 


The  following  table  gives  the  dates  of  tetrad  aud  pollen  formation  as 
well  as  the  size  of  the  pollen  grains  of  several  varieties  being  grown  in  the 
Experiment  Station  orchard. 

TABLE  No.  IV 


• 

> 

•o 

i1 

•z 

a 
a 
a. 

o 

H 

O 

a 

t| 

fl)   (4 

<2  o 

!« 
1 

Q 

*i 

ii 

11 

Q 

1 

Q 

No.  days  from 
pollen  form 
pollen  shed 

Randal    

4/13 

1 

4/17 

4 

48 

5/1 

14 

\elson              

4/11 

1 

4/13 

2 

48 

4/29 

16 

Allen 

4/13 

1 

4/14 

1 

48 

5/1 

17 

Robson    

4/14 

1 

4/17 

3 

44 

5/1 

14 

San  Saba    
Mobile 

4/14 

1 
1 

4/17 
4/16 

r> 

44 
48 

5/2 
5/3 

15 
17 

Jerome    
Rome  
Centennial 

4/14 
4/13 
4/13 

1 
1 
1 

4/16 
4/14 
4/14 

O 
1 

1 

48 
48 

48 

5/1 
5/1 

5/2 

15 
17 
18 

Man  t  u  ra    

1 

4/14 

48 

5/1 

17 

Beverage   Triumph. 

4/14 

1 

2 

4/17 
4/19 

3 

44 
51 

5/1 

5/9 

14 
20 

Pabst 

1 

4/17 

48 

5/3 

16 

Washington   
Schley 

4/26 

1 
2 

4/19 
4/28 

2 

51 
51 

5/1 
5/13 

12 
17 

Van  Deman    

4/22 

2 

4/24 

o 

51 

5/10 

16 

Stuart          

4/21 

o 

4/22 

1 

48 

5/11 

19 

Teche 

4/21 

2 

4/22 

1 

51 

5/13 

21 

Young   
Appomattox    
President 

4/24 
4/19 

2 
2 
2 

4/26 
4/21 
4/22 

2 
2 

51 
51 
51 

5/11 
5/8 
5/11 

15 
17 
19 

Atlanta 

2 

4/22 

51 

5/11 

19 

Russell      

4/22 

2 

4/24 

2 

51 

5/11 

17 

Frotscher         

4/22 

2 

4/26 

4 

51 

5/12 

16 

Curtis 

4/22 

r> 

4/26 

4 

48 

5/14 

18 

Pan  American  
Hickory 

4/22 

2 

1 

4/26 

4 

51 
55 

5/12 

16 

Japan  Walnut  
Snanlsh    Chestnut.. 

38 
17x10 

Two  GROUPS  OF  THE  HICORA  PECAN  139 


The  Relation  of  the  Two  Groups  to  'Self-Sterility 

The  results  of  our  work  thus  far  leave  little  doubt  that  self-sterility  in 
pecans  is  due  primarily  to  the  interval  in  time  between  the  receptive  stage 
of  the  pistillate  flowers  and  the  shedding  of  the  pollen. 


Left  to  right  —  Stigmas  up  —  1.  Nelson  —  receptive;   2.  Pabst  —  just  entering  receptive 

stage;     3.    Jerome  —  just  past  receptive  stage;     4.    Frotscher  —  receptive 

stage  past,  and  stigma  dried.     Magnified  2%  times  natural  size. 

Those  varieties  in  Group  I  where  the  pistillate  flowers  are  receptive  at 
the  time  the  pollen  sheds,  present  no  difficulties  in  the  problem  of  self-steril- 
ity. But  those  varieties  in  Group  II  where  the  pistillate  flowers  are  past 
the  receptive  stage,  and  the  stigmas  dried  before  the  first  pollen  sheds  are 
necessarily  self-sterile  in  varying  degrees  according  to  the  persentage  of 
dried  or  calloused  stigmas  on  the  tree  before  the  pollen  begins  to  shed. 
These  points  were  investigated  by  the  usual  methods  of  field  observations, 
bagging,  and  crossing. 

In  our  field  observations  of  Group  I,  as  will  be  seen  by  referring  to 
Tables  1,  2  and  3,  all  those  varieties  in  Group  I  shed  their  first  pollen  at 
about  the  same  time  that  the  pistillate  flowers  become  receptive,  thus  giv- 
ing ample  opportunity,  in  most  cases,  for  the  pistillate  flowers  to  be  ferti- 
lized by  pollen  from  the  same  tree.  We  found  that  the  stigmas  of  the 
pistillate  flowers  remained  in  a  fresh,  undried  condition  for  a  period  of 
several  days,  considerably  longer  than  those  in  Group  IT.  However,  all  do 
not  become  receptive  at  the  same  time  and  we  found  that  there  is  some 
danger  of  the  varieties  of  Group  I  shedding  their  pollen  too  early  for  pol- 
linating all  their  own  pistillate  flowers,  i.  e.  those  coming  into  the  receptive 
stage  late.  Observations  showed  that  a  number  of  stigmas  of  the  Alley  and 
the  Randall  varieties  were  still  fresh  and  vicid  after  practically  all  the 
catkins  of  staminate  flowers  had  dried  and  fallen.  This  indicates  that  it 
is  possible,  at  least  during  some  seasons,  for  the  pollen  of  the  two  varieties 
to  shed  before  all  the  pistillate  flowers  are  fertilized.  This  is  especially 
true  if  there  should  be  heavy  winds  and  rains  at  the  time  the  majority  of 
the  anthers  are  dehiscing,  for  during  such  weather  the  pollen  is  either 
washed,  or  blown  away.  There  is  also  some  danger  of  the  pollen,  hanging 
in  the  old  and  dried  catkins,  not  remaining  viable  for  fertilizing  the  late 
pistillate  flowers  where  such  pollen  is  exposed  to  the  weather  conditions. 
To  make  a  test  of  this  point,  on  May  15,  1916,  pollen  was  collected  from  the 
dried  catkins  hanging  on  the  trees  of  the  Alley,  Jerome,  and  Nelson  varieties 
and  the  usual  germination  test  made.  None  of  this  pollen  germinated  even 
though  the  same  varieties  gave  high  germination  tests  about  ten  days 
previously  when  the  pollen  was  taken  directly  from  the  dehiscing  anthers. 


140 


GEORGIA  EXPERIMENT  STATION 


Branch  from  a  Stuart  tree  showing:  young  Catkins  intermingled 
with  the  larger  ones.  This  gives  a  long  period  of  pollen  shed- 
ding. Unfortunately  little  of  this  is  found  among  the  early 
blooming  varieties. 

In  Group  II  by  referring  to  Tables  1,  2  and  3,  it  will  be  noticed  that  the 
interval  between  the  receptive  stage  of  the  stigmas  and  the  first  shedding 
of  the  pollen  varied  from  four  to  nine  or  more  days,  thus  making  the  pol- 
lination of  the  stigmas  by  pollen  from  the  same  tree  rather  difficult.  How- 
ever, the  difficulty  in  drawing  definite  conclusions  from  this  lies  in  the  fact 
that  in  making  field  observations  it  is  very  difficult  to  determine  just  when 
the  stigmas  of  pecans  become  receptive  and  the  exact  time  they  pass  the  re- 
ceptive stage.  Those  stigmas  of  the  pistillate  flowers  that  were  bagged  and 
pollen  excluded,  dried  or  calloused  at  about  the  same  time  as  those  bagged 
and  pollinated.  In  the  further  pursuance  of  the  experiment  an  effort  will 
be  made  to  determine  these  points.  To  obviate  this,  however,  we  recorded 
the  dates  when  the  stigmas  dried  and  calloused  over  sufficiently  to  leave 
no  doubt  that  the  receptive  stage  had  been  passed.  From  this,  it  will  be 
seen  that  the  varieties  of  Group  II  had  their  stigmas  to  dry  and  callous 
over  from  one  to  five  days  before  the  first  pollen  shed,  thus  practically  pre- 
cluding the  pollinating  of  the  stigmas  by  pollen  from  the  same  tree.  How- 
ever, in  the  case  of  the  Curtis  and  the  Stuart,  a  considerable  number  of 
belated  pistillate  flowers  showed  fresh  stigmas  on  the  date  the  first  pollen 
was  shed.  In  such  cases  when  these  varieties  are  grown  alone,  we  would 
not  expect  complete  sterility,  but  a  light  crop. 


Two  GROUPS  OF  THE  HICORA  PECAN 


141 


An   Alley   tree   showing    bags    in   place. 


142  GEORGIA  EXPERIMENT  STATION 

Sterility  Avoided  Through  Mechanical  Injury  to  Catkins 

It  was  observed  that  catkins  of  staruinate  flowers  broken  off  by  the 
wind,  or  by  other  mechanical  agencies,  and  left  hanging  in  the  trees  where 
they  became  more  or  less  dried,  shed  pollen  several  days  before  the  normal 
dehisence  of  the  anthers.  To  determine  whether  or  not  such  pollen  was 
viable,  some  catkins  from  a  Curtis,  and  a  Stuart  tree,  three  and  four  days 
respectively  before  the  first  pollen  was  normally  shed,  were  taken  to  the 
laboratory  and  allowed  to  dry  at  room  temperature  for  twenty-four  hours 
at  which  time  the  pollen  had  begun  to  shed.  The  usual  germinatioH  tests 
were  made  of  this  pollen  with  the  result  that  50  per  cent  of  the  Curtis  and 
62  per  cent  of  the  Stuart  pollen  germinated.  While  these  catkins  were 
pulled  from  the  trees  two  and  three  days  respectively  before  the  first  pollen 
shed,  it  is  probable  that  they  were  pulled  four  or  even  five  days  before  they 
would  have  shed  their  first  pollen  normally  as  the  most  forward  catkins  of 
the  trees  were  probably  not  pulled.  Such  results  make  it  possible  that  vari- 
eties of  Group  II  could  be  partially  fertilized  from  pollen  of  catkins  receiv- 
ing some  mechanical  injury  a  few  days  before  the  pollen  shed  normally. 
Such  trees,  otherwise,  might  be  wholly  self-sterile. 

Parthenogenesis  Indicated 

Pecans  are  like  several  other  nuts  in  presenting  many  difficulties  in 
bagging  and  cross  pollinating. 

Morris  (7)  called  attention  to  the  development  of  seediugs  grown  from 
seedling  Chinquapins,  the  flowers  of  which  were  bagged  to  prevent  pollina- 
tion. "Subsequently  check  experiments  indicate  that  the  chinquapin  will 
develop  nuts  freely  without  pollen ;  and  that  the  bitter  nut  hickory,  shag 
bark  hickory,  and  pig  nut  will  develop  nuts  sparingly  without  pollen." 

Pistillate  flowers  of  the  pecan  are  terminal  and  appear  on  the  current 
year's  growth  rather  early  in  the  season.  At  the  time  the  bags  are  .to  be 
put  on  there  are  a  number  of  compound  leaves  somewhat  shielding,  and  just 
posterior  to  the  embryonic  pistillate  flowers  that  go  into  the  bag  readily  at 
the  time,  but  increase  in  size  so  rapidly  that  the  bag  is  soon  overcrowded. 
An  attempt  to  remove  these  small  leaves  before  bagging  usually  results  in 
such  injury  to  the  young  terminal  that  the  pistillate  flowers  fail  to  develop. 
Again  the  young  growth  of  the  pecan  is  very  sensitive  to  any  abnormal  con- 
ditions of  air,  light,  or  temperature,  and  is  unable  to  withstand  even  very 
light  mechanical  injuries.  The  common  yellow  paper  bags  are  almost  fatal 
to  the  terminals  if  allowed  to  remain  on  very  long.  Cloth  bags  that  are 
thin  enough  to  allow  the  bagged  terminals  to  grow  under  even  approxi- 
mately normal  conditions  are  liable  to  admit  drifting  pollen  and  thus  make 
the  results  uncertain.  Cloth  bags  sufficiently  closely  woven  to  keep  out 
pollen  are  likely  to  injure  the  terminals  to  only  a  little  less  degree  than 
paper  bags.  Therefore,  the  very  thinest  and  lightest  white  cloth  that  will 
exclude  pollen  seems  to  be  best  for  bagging  the  terminals. 

In  1915  we  bagged  14  clusters  of  pistillate  flowers  on  a  ten-year-old 
Stuart  tree,  using  thin,  white  and  closely-woven  lawn  cloth  for  the  bags. 
The  fourteen  clusters  of  pistillate  flowers  were  treated  as  follows : 

(1)  All  catkins  of  staminate  flowers  removed  and  the  cloth  bag  put  on 
before  the  pistillate  flowers  became  receptive.     No  pollen  was  applied  to 
the  stigmas  and  the  bag  was  allowed  to  remain  on  until  several  days  after 
the  stigmas  dried  and  nut  growth  had  begun.     This  cluster  produced  two 
nuts,  one  appeared  normally  filled,  and  the  other  was  a  mere  shell. 

(2)  The  bag  was  put  on  before  the  pistillate  flowers  were  receptive  and 
before  any  pollen  had  shed,  enclosing  both  pistillate,  and  staminate  flowers 
in  the  bag.    The  bag  injured,  somewhat,  the  new  growth,  and  no  nuts  were 
produced. 

(3)  Bagged  as  was  number  two,  and  pollinated  with  pollen  from   a 
Robson  tree  when  stigmas  appeared  receptive.     No  nuts  produced. 


Two  GROUPS  OF  THE  HICORA  PECAN  143 

(4)  Implicate  of  No.  2,  inclosing  both  sex  of  flowers.    This  cluster  pro- 
duced one  nut  that  was  normally  filled. 

(5)  Duplicate  of  No.  2.    No  nuts  formed. 

(6)  The  catkins  were  cut  from  this  branch  and  the  cluster  of  pistillate 
flowers  bagged  as  in  No.  1.    One  abnormally  formed  nut,  which  was  a  mere 
shell,  was  produced.     It  was  about  one-fourth  normal  size  and  was  sharp 
pointed. 

(7)  Emasculated  and  bagged  as  No.  1.    This  cluster  produced  one  nut 
that  seemed  normal  excepting  that  it  failed  to  ripen  on  time. 

(8)  Emasculated  and  bagged  as  No.  1.    Produced  three  normal  nut« 

(9)  Bagged  inclosing   sexes  of   flowers  as  No.   2  and  pollinated  with 
pollen   from   Robsou   when   stigmas  appeared   receptive.     One  abnormally 
formed  shell  lacking  any  embryo  was  produced. 

(10)  Same  as  No.  9  excepting  that  two  instead  of  one,  half  size  shells 
without  embryo  were  formed. 

(11,  12,  and  13)   Bagged  same  as  No.  2,  but  no  nuts  were  produced. 

(14)  Emasculated  and  not  pollinated  same  as  No.  1.  This  cluster  pro- 
duced one  nut  well  filled,  but  was  only  approximately  half  size  for  this 
variety,  and  also  one  small  shell  without  an  embryo. 

We  bagged  large  numbers  of  flower  clusters  of  about  twenty  other 
varieties  in  1916,  and  got  results  very/  similar  to  those  above  reported.  The 
bags  were  put  on  with  great  care  and  strict  precaution  taken  to  prevent 
pollination  other  than  that  applied  by  hand  as  planned;  yet  we  find 
nuts  appearing  in  bags  that  were  put  on  before  the  pistillate  flowers  were 
receptive  and  no  pollen  allowed  to  enter.  This  condition  indicates  that 
parthenogenesis  exists  in  pecans  as  reported  by  Morris  (7)  in  three  species 
of  hickories,  and  the  chinquapin. 

Hickory-Pecan  Hybrids 

The  entire  list  of  tree  species  that  are  capable  of  being  hybridized  has 
not  yet  been  determined.  Babcock  (6)  crossed  the  native  walnut  of  South- 
ern California  (Juglans  californica)  as  the  female  parent  and  the  coast  live 
oak  (Quercus  agrifolia)  and  one  of  the  oak  hybrids  as  a  male  parent.  Nuts 
from  both  these  crosses  produced  plants.  Some  pecan  propagators  have* 
propagated  and  disseminated  nut  trees  which  are,  in  habits  of  growth,  de- 
partures from  the  hickory  and  said  to  be  hybrids  between  the  hickory  and 
the  pecan.  These  have  been  given  the  name  "Hican." 

The  exact  origin  of  these  hicans  seems  not  to  be  definitely  known.  How- 
ever, they  vary  as  much  from  the  pecan  as  from  the  hickory  and  are  very 
probably  hybrids  between  the  two  species.  The  chief  differences  between 
these  supposed  hybrids  and  the  pecan  is  that  they,  like  the  hickory,  pro- 
duce their  catkins  only  at  the  base  of  the  current  year's  growth,  while  the 
pecan  sends  out  its  catkins  at  several  nodes  along  the  preceding  year's 
growth. 

Hickories  as  Pollinators  for  Pecans 

Hickory  trees  on  the  Experiment  Station  grounds,  like  pecans,  could  be 
divided  into  early  and  late  staminate  flowering  groups.  However,  they 
differ  from  the  pecan  in  that  the  catkins  are  borne  only  at  the  base  of  the 
new  growth  and  none  are  conspicuously  bracted  as  are  the  catkins  in  Group 
II  of  pecans.  The  two  groups  among  hickory  trees  do  not  seem  to  be 
confined  strictly  to  species  as  we  found  both  late  and  early  bloomers  among 
trees  of  Hicora  glabra,  and  what  appears  to  be  hybrids  between  Hicora 
fflabra  and  Hicora  alba.  The  late  blooming  hickories  shed  their  pollen  at 
about  the  time  that  the  pistillate  flowers  of  varieties  of  Group  IT  of  pecans 
are  receptive. 


144 


GEORGIA  EXPERIMENT  STATION 


Two  twigs  front  hickory  trees.  One  on  left  has  shed  most  of  its  pollen  while  the 
pistillate  flowers  are  hardly  receptive.  One  on  right  has  shed  no  pollen  and 
the  stigmas  of  the  pistillate  flowers  dried  and  growth  of  the  young  nuts  started. 

Going  on  the  hypothesis  that  the  hickory  aud  the  pecan  will  hybridize, 
we  attempted  to  make  some  crosses  between  the  two  species  in  1916.  Three 
clusters  of  pistillate  flowers  on  a  Stuart  tree  were  bagged  before  they 
were  receptive  and  later  pollinated  in  their  receptive  stage  with  hickory 
(Hicora  glabra)  pollen.  From  these  crosses  we  secured  two  nuts,  yet  in 
view  of  our  1915  experiences  we  are  not  sure  whether  these  nuts  are  the 
.result  of  the  hickory-pecan  cross  or  whether  they  are  parthenogeuic  devel- 
opments. If  these  nuts  are  the  result  of  the  hickory  pollen  we  have  some 
explanation  to  offer  for  pecan  varieties  of  Group  II  producing  nuts  in  close 
proximity  to  hickory  trees  when  they  would  be  either  partially  or  wholly 
self  sterile  if  grown  in  absence  of  pollen  other  than  their  own  production. 

Varieties  Recommended  for  Planting 

If  varieties  of  Group  II  are  self-sterile  when  planted  alone,  varieties  of 
Group  I  should  be  planted  in  close  proximity  to  insure  successful  pollination. 

Before  making  recommendations  of  methods  for  arranging  the  varieties 
of  the  two  groups  in  planting  so  as  to  make  pollination  more  certain,  we 
thought  it  best  to  supplement  varietal  data  from  the  Experiment  Station 
plat  with  the  recommendations  of  commercial  pecan  growers  in  different 
sections  of  Georgia  as  well  as  from  a  few  sections  of  neighboring  states. 
This  is  done  for  two  reasons,  first,  because  the  Experiment  Station  is 
located  in  the  Piedmont  section  of  the  State  where  some  commercial 
varieties  are  thought  not  to  do  well ;  and  second,  for  the  purpose  of  eliminat- 
ing personal  preferences  by  getting  preferences  of  a  considerable  number 
of  growers. 

To  secure  this  data  a  circular  letter  was  sent  to  sixty  pecan  growers 
with  the  request  that  they  name  six  varieties  best  suited  to  their  respective 
localities.  In  some  instances  more  than  one  choice  is  given  from  a  locality 
which  shows  personal  preferences  of  different  growers.  Most  of  the  grow- 
ers gave  the  varieties  in  order  of  preference.  The  following  table  gives 
the  varieties  from  the  different  localities  in  the  same  order  as  given  by  the 
growers.  \ 


Two  GROUPS  OF  THE  HICORA  PECAN 


145 


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146 


GEORGIA  EXPERIMENT  STATION 


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TWO  GROUPS  OF  THE  HlCOKA   PECAN  147 

From  the  above  table  it  will  be  observed  that  Schley,  Stuart,  Delnias, 
Van  Deman  and  Moneymaker  of  Group  II  are  very  popular  among  the 
growers  while  Success,  Pabst,  and  Alley  are  popular  varieties  of  Group  I. 
Yet  there  are  other  varieties  in  the  table  that  are  preferred  in  varying 
degrees  and  should  be  planned  for  in  grouping  for  successful  pollination. 

Below  we  give  a  list  of  the  varieties  in  each  group  that  have  come 
under  our  observation.  From  these  the  grower  can  select  such  as  he 
likes  and  group  them  so  that  the  varieties  of  Group  I,  the  early  bloomers, 
can  be  so  planted  as  to  serve  as  pollinators  for  varieties  of  Group  II,  the 
late  bloomers;  or  cions  from  varieties  of  one  group  may  be  top  worked 
onto  a  few  limbs  of  the  other  group  and  in  this  way  one  tree  will  rep- 
resent both  groups. 

Varieties  of  Pecans 

Group  I.  '                                              Group  II. 

Alley  Appomattox 

Beverage  Triumph  Atlanta 

Centennial  Bradley 

Georgia  Giant  Capital 

Haven  Curtis 

Jerome  Delmas 

Mantura  Frotscher 

Mobile  Hadley 

Moore  Moneymaker 

Nelson  Pan-American 

Pabst  President 

Randal  Russell 

Robson  Russell  No.  2 

Rome  Stuart 

San  Saba  Teche 

Success  Van  Deman 

Washington  Waukenah 

Young 

Below  is  given  an  outline  suggesting  methods  of  planting  the  trees  of 
the  two  groups : 

Group   1 X  X  X  X  X  X  X 

Group   2 X  X  X  X  X  X  X 

Group   2 X  X  X  X  X  X  X 

Group   1 X  X  X  X  X  X  X 

Group   2 X  X  X  X  X  X  X 

Group   2 X  X  X  X  X  X  X 

Group   1 X  X  X  X  X  X  X 

We  give  two  rows  to  be  planted  to  varieties  of  Group  II  to  each  one 
row  of  Group  I,  primarily  for  the  reason  that  most  commercial  growers 
give  first  and  second  place  to  the  varieties  of  Group  II. 

In  grouping  varieties  including  Alley  and  Moneymaker,  it  is  well  that 
these  two  varieties  be  planted  near  each  other  for  the  reason  that  Alley 
sheds  its  catkins  before  all  the  pistillate  flowers  pass  the  receptive  stage  and 
that  the  Moneymaker  is  one  of  the  earliest  bloomers  of  Group  II  and 
will  serve  as  a  pollinator  for  the  Alley. 

CONCLUSIONS 

1.  Varieties  of  pecans  can  be  divided  into  two  distinct  groups  based  on 
their  floral  characters. 

2:  Varieties  of  Group  I  shed  their  pollen  at  about  the  same  time  the 
majority  of  the  pistillate  flowers  become  receptive. 


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Thi«  ••-•"k  is  DUE  on  the  last  date  stamped  below 


148  GEORGIA  EXPERIMENT  STATION 

3.  Varieties  of   Group   II    shed   their   first   pollen   after   most   of  the 
pistillate  flowers  pass  through  the  receptive  stage. 

4.  On  the  whole,  the  varieties  of  Group  I  are  apt  to  be  self-fertile,  while 
those  of  Group  II  are  apt  to  be  self-sterile. 

5.  Varieties  of  both  groups  product  viable  pollen. 

6.  Phenological   data   from   varieties   grown   in    South    Georgia   agree 
fairly  closely,  as  regards  the  two  groups,  with  that  from  the  varieties  at  the 
Experiment  Station. 

7.  Native  hickory  trees  in  the  vicinity  of  Experiment,  Ga.,  could  be 
divided  into  early  and  late  staniinate  flowering  groups. 

8.  It  is  probable  that  the  hickory  will  serve  as  a  pollinator  for  the 
pecan. 

9.  Self-sterility  of  a   variety   may   be   expected   in   proportion   to   the 
interval   between   the   receptive   stage   of   the   pistillate   flowers   and   the 
shedding  of  the  pollen 

10.  Mechanical  injury  to  catkins  before  the  date  of  normal  shedding  of 
pollen  may  partially  prevent  self-sterility  among  varieties  of  Group  II. 

11.  Parthenogenesis  in  pecans  is  indicated. 

12.  Varieties  from  Group  II  should  be  planted  in  close  proximity  to 
varieties  from  Group  I  to  insure  successful  pollination. 

ACKNOWLEDGMENT 

Grateful  acknowledgment  is  due  the  following: 

Mr.  J.  Slater  Wight,  of  Cairo,  Ga.,  for  supplying  phenological  data 
given  in  Table  3. 

Mr.  H.  C.  White,  Putney,  Ga. ;  Mr.  G.  H.  Tomlinson,  Putney,  Ga. ; 
Mr.  J.  B.  Wight,  Cairo,  Ga. ;  Mr.  B.  W.  Stone,  Thomasville,  Ga.,  tor 
allowing  the  use  of  their  orchards  for  making  observations  and  supplying 
floral  material  for  laboratory  studies. 

A  large  number  of  growers  in  various  sections  of  the  pecan  belt  for 
making  recommendations  of  varieties  suitable  for  their  respective  localities. 

Dr.  B.  B.  Higgins,  Botanist  and  Plant  Pathologist  of  this  Experiment 
Station  for  making  drawings  of  tetrad  (Fig.  6)  ;  for  making  microphoto- 
graph  (Fig.  4)  and  for  helpful  suggestions  and  criticisms  of  the  manuscript. 

REFERENCES 

( 1 )  Stuckey,  H.  P.    Ga.  Exp.  Sta.  Ann.  Kept.    1915. 

(  2  (  Bailey,  L.  H.    Report  of  the  Horticulturist.    Mich.  Agr.  Clo.  Bull.  31:1-96.    1887. 

The  Cultivated  Native  Plums  and  Cherries.     N.  Y.  Cornell  Exp. 

Sta.  Bull.  38:1-73.     1892. 
(  3  )  Beach,  S.  A.    The  Self -Pollination  of  the  Grape.    Gard.  and  For.  5:451-452.   1892. 

-  Notes  of  Self-Pollination  of  the  Grape.    N.  Y.  State  Exp.  Sta.  Ann. 
Kept.  597-606.    1892. 

The  Fertilization  of  Flowers  in  Orchards  and  Vineyards.     N.  Y. 

Sta.  Ann.  Kept.  13 :633-648.    1894. 

-  Production  of  Grapes  as  Affected   by  Self- Fertilization  of  Their 
Blossoms.    N.  Y.  State  Sta.  Ann.  Kept.  14:320-325.    1895. 

-  Self- Fertility  of  the  Grape.  N.  Y.  State  Exp.  Sta.  Bull.  157:397-441. 

-  Fertilizing  Self-Sterile  Grapes.     N.  Y.  State  Exp.  Sta.  Bull.  169: 
331-371. 

(  4  )  Waite,  M.  B.     The  Pollination  of  Pear  Flowers.     U.  S.  Dept.  Agr.  Div.  Veg. 
Phys.  Path.  Bull.  5:1-86. 

-  Sterility  in  Japanese  Plums.    Am.  Agr.  75:112.    1905. 

(5)  Waugh,  F.  A.    The  Pollination  of  Plums.    Am.  Pom.  Soc.  Kept.  25:86-94. 

-  The  Pollination  of  Plums.    Vt.  Exp.  Sta.  Bull.  53:45-65. 

-  Problems  in  Plum  Pollination.    Vt.  Exp.  Ann.  Kept.  11:238-262. 
Further  Work  in  Plum  Pollination.    Vt.  Exp.  Sta.  Ann.  Kept.    13: 

">55-362. 

-  Pollination  of  Apples.    Vt.  Exp.  Sta.  Ann.  Kept.  13:362-366. 

(6)  Babcock,  E.  B.     Walnut-Oak  Hybrid  Experiments.     Amr.  Breeders'  Mag.   3: 

200-202.     1910. 

(  7  )  Morris,  R.  T.    TTnusual  Methods  of  Propagating  Nut  Trees.     North.  Nut  Grow- 
ers' Assoc.  Proc.  4:45-48.    1913. 

(  8  )  Ramsey.  F.  T.     My  Experience  with  English  Walnuts.     The  Nut  Grower,  XV. 

(  9  )  Berckmans,  P.  J.    Ga.  State  Hort.  Soc.  Proc.    27th  Ann.  Rept :  P.  46. 
(10)  Lewis,  C.  I.    Walnut  Culture  in  Western  Oregon.    1916. 


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